1. Field of the Invention
The present invention relates to a transceiver for radio communications, and more particularly to a radio transceiver with an integrated transmitter and receiver for transmitting and receiving microwaves or higher frequency electromagnetic waves, the radio transceiver being one of a series of device products having different transmission output power capacities.
Radio transceivers having an integrated transmitter and receiver are characterized by small size. Because radio transceivers are small in size, they may be positioned close to an antenna or integrally combined with an antenna, and consequently, the radio device requires no station buildings or shelters and hence can be installed at a low cost. The size of such radio transceivers is an important factor to be considered. Since the size of a radio transceiver varies according to the size of a cooling radiator, the size of the transceiver varies in proportion to the transmission output power capacities of the transceiver. It is therefore increasingly important to produce a series of models having different transmission output power capacities.
2. Description of the Related Art
Radio transceivers having an integrated transmitter and receiver for transmitting and receiving radio-waves such as microwaves or higher frequency electromagnetic waves have been available in a series of models which are operable in the same frequency band and the same signal processing format and have different transmission output power capacities. There have heretofore been three alternative design approaches to produce such a series of radio transceivers.
The first process is to individually design radio transceivers with different transmission output power capacities. Generally, the total quantity of heat generated by a radio transceiver depends greatly on the output power of a transmission power amplifier thereof. Therefore, the area of a heat radiating plate and the size of the device vary in proportion to the magnitude of the output power of the transmission power amplifier. According to the first approach, therefore, all the dimensions including the length, width, and height of the device housing, and the size of the heat radiating plate can be designed to optimally meet the output power requirement of the transmission power amplifier.
According to the second design principle, the basic device design is carried out with respect to a type having a highest transmission output power capacity, and a type having a lower transmission output power capacity is manufactured by replacing a power amplifier in the basic type with a simple transmission line. This design approach allows the use of a device housing and heat radiating plate of the same sizes in models having different transmission output power capacities.
More specifically, a transceiver having a smaller transmission output power capacity is shown in cross section in FIG. 1, and a transceiver having a greater transmission output power capacity is shown in cross section in FIG. 2. In FIGS. 1 and 2, heat radiating housing case 1 accommodates therein transmission module 2a or 2b, reception module 3, common circuit and IDU (indoor unit) communication signal combining circuit 4, and transmission and reception shared circuit 5.
The transceiver having a greater transmission output power capability shown in FIG. 2 has a power amplifier 7 disposed in transmission module 2b. Heat radiating housing case 1 shown in FIG. 2 has a maximum radiator area and a size which are selected to dissipate an amount of heat which is produced by the maximum electric power consumption to meet a maximum transmission output power requirement. The transceiver having a smaller transmission output power capability shown in FIG. 1 has transmission line 6 instead of power amplifier 7 in transmission module 2a. The heat radiating housing case 1 shown in FIG. 1 is, however, identical to the heat radiating housing case 1 shown in FIG. 2.
According to the third design plan, a power amplifier is attached as an independent exterior unit to a device casing to accommodate thereby various models having different transmission output power capacities. With the third design approach, the size of the device housing of a transceiver with a minimum transmission output power requirement can be used as a base size.
The first design principle is disadvantageous in that the device casing and components are not sufficiently standardized, resulting in an increase in the cost of those products in the series which do not enjoy high sales, as well as an increase in the time required by the manufacturing process before shipment.
Better standardization can be achieved by the second design program. However, since the basic design is based on the a transceiver having a greater transmission output power capacity, the heat radiating housing case 1 are large, as is the size of the device. No substantial economic problem arises if a larger proportion of models providing larger transmission output power are sold, but if more models providing smaller transmission output power are sold, the second design approach is not economical.
More specifically, since a transceiver having a smaller transmission output power capacity shown in FIG. 1 has no power amplifier, the entire electric consumption of the device is low and the device does not need a large radiator. However, the size of the device remains the same as a device with the larger transmission output power capacity because the basic model is the model with the higher output power. Accordingly, standardization based on the higher-out-put-power model is not beneficial for the lower-output-power model. If there is a greater demand in the market for the lower-output-power model, the extra cost involved in producing a device in an overly large case may result in a reduced ability to compete against another manufacturer's smaller and less expensive designs.
The second design process is also problematic if it should become necessary to produce a model having a higher transmission output power capacity than can be handled by the original design. When such a model is required, since the existing device housing lacks the physical space to accommodate a heat radiator for cooling a power amplifier of greater output power, it is necessary to redesign a transceiver with a greater transmission output power capability together with its housing.
A transceiver designed according to the third design approach is complex in structure. Specifically, because one antenna and one indoor unit connection cable are shared by the transmission and reception functions, it is necessary to take transmission output power out of the device, amplify the transmission output power with the exterior amplifier unit, and return the amplified transmission output power back into the device to supply a transmission and reception shared circuit. Inasmuch as the transceiver is compact and has a horn attached directly in combination with an antenna reflector, the exterior amplifier unit cancels out any merit provided by the integration of transmitter and receiver.
According to the third design principle, furthermore, because the length of the cable connected to the exterior amplifier unit is long compared with the wavelength, a standing wave is produced introducing ripples into the frequency characteristics if the voltage standing wave ratio in the transmission and reception shared circuit, the transmission module, the power amplifier, etc. is not sufficiently small. To prevent the generation of such a standing wave, it is effective to add an irreversible circuit element called an isolator to each module. However, adding such an irreversible circuit element is expensive.